Electrochemical and biological response oftitanium (cp-Ti) after silicon ion implantation

K.M. DeenDepartment of Metallurgy & Materials Engineering, CEET, University of the Punjab, Lahore, Pakistan and Department of Materials

Engineering, The University of British Columbia, Vancouver, Canada

A. FarooqDepartment of Metallurgy & Materials Engineering, University of the Punjab, Lahore, Pakistan

M. Rizwan and A. AhmadDepartment of Metallurgical and Materials Engineering, University of Engineering and Technology (UET), Lahore, Pakistan, and

W.HaiderSchool of Engineering and Technology, Central Michigan University, Mt. Pleasant, Michigan, USA

AbstractPurpose – This study/paper aims to the authors applied low “Si” ions dose over cp-Ti-2, and the potent dose level was optimized for adequatecorrosion resistance and effective proliferation of stem cells.Design/methodology/approach – The cp-Ti surface was modified by silicon (Si) ions beam at 0.5MeV in a Pelletron accelerator. Three differention doses were applied to the polished samples, and the surface was characterized by XRD and AFM analysis.Findings – At moderate “Si” ion dose (6.54� 1012 ions-cm�2), the potential shifted to a noble value. The small “icorr” (1.22 mA.cm�2) andrelatively large charge transfer resistance (43.548 kX-cm2) in the ringer‘s lactate solution was confirmed through Potentiodynamic polarization andimpedance spectroscopy analysis. Compared to cp-Ti and other doses, this dose level also provided the effective proliferation of mesenchymal stemcells.Originality/value – The dosage levels used were different to previous work and provided the effective proliferation of mesenchymal stem cells.

Keywords Metals, Corrosion, Surface, Ion implantation

Paper type Research paper

Introduction

The commercially pure titanium (cp-Ti) is widely used inorthopedics, osteosynthesis and dental implants due to itscomparable mechanical strength to human bones and goodcorrosion resistance in the biological environment (Espositoet al., 1999; Lopez et al., 2003; Strietzel et al., 1998; Dearnleyet al., 2003). The dissolution of TiO2 passive film, the release ofmetal ions, reactions of amino acids and inorganic species withtitanium implants has been reported in the literature (Hosseiniet al., 2007;Mu et al., 2000; Takemoto et al., 2012).Many surface modification methods have been adopted to

enhance corrosion resistance and biocompatibility of titaniumi.e. thermal oxidation (Alonso et al., 2003), ion implantation(Rautray et al., 2011; Rizwan et al., 2014), anodic oxidation(Song et al., 2007), sol-gel (Haddow et al., 1996; Gan et al.,2005), plasma spray (Kweh et al., 2002), chemical passivation(Masmoudi et al., 2006), sandblasting (Jiang et al., 2006), laser

treatment (Carpene et al., 2005) and electrolytic polishing(Guilherme et al., 2005).Among these methods the “ion implantation” is ultra-clean

and quasi-equilibrium process by which surface layers of thesubstrate can be modified (Rautray et al., 2011). To increasecorrosion resistance and biocompatibility of titanium, severalions e.g. Nitrogen (Rizwan et al., 2014; Becdelievre et al., 1988;Krupa et al., 1996; Leitao et al., 1995), Palladium, Iron, Xenon(Schultze et al., 1985), Krypton, Argon, and Neon (Braceraset al., 2014) have been applied.Meisner et al., (2012) implanted high dose (2�1017 ions.

cm�2) Silicon (Si), Titanium, and Zirconium ions over 0NiTi0

alloy to enhance its biocompatibility and proliferation ofmesenchymal stem cells. Baszkiewicz et al. (Baszkiewicz et al.,2000) reported severe localized corrosion and adversesubsurface structural change on Ti6Al4V alloy after a high doseof ‘Si’ ions implantation. The lowest ‘Si’ ions (0.5�1017ions.cm�2) dose was reported as least susceptible to corrosion in 0.9per cent NaCl solution. This proclaimed ‘Si’ ions fluence isconsidered large enough which could induce localizedstructural changes at the surface of the substrate. It is assumed

The current issue and full text archive of this journal is available onEmerald Insight at:https://www.emerald.com/insight/0003-5599.htm

Anti-Corrosion Methods and Materials67/1 (2020) 1–6© Emerald Publishing Limited [ISSN 0003-5599][DOI 10.1108/ACMM-03-2017-1771]

The kind support and discussion with Dr Raiz Ahmad, Director, Centerfor Advanced Studies for Physics, GC University, Lahore, Pakistan, isacknowledged.

Received 9 March 2017Accepted 1 March 2019

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that even low dose of ‘Si’ ions could be beneficial to enhancecorrosion resistance of titanium. Therefore, in this preliminarystudy, we applied low ‘Si’ ions dose over cp-Ti-2 and the potentdose level was optimized for adequate corrosion resistance andeffective proliferation of stem cells.

Experimental

The cp-Ti-2 samples (10�15� 5mm) were ground up to 1000grit size, polished (0.1mm; diamond paste) followed byultrasonic cleaning in the acetone and ethanol separately. The0.5MeV ‘Si’ ions beam was focused on applying different iondoses at the polished samples in a vacuum chamber (10�6 mbar)of Pelletron accelerator. By adjusting the beam current andfluence time, three ion doses Si-11 (6.23� 1011ions.cm�2), Si-12 (6.54� 1012ions.cm�2) and Si-13 (3.27� 1013ions.cm�2)were applied. The X-ray (Cu-Ka radiations) diffraction(PANalytical) (XRD) patterns were obtained within 20°-70° at0.05°/sec step size. The surface morphology was examinedthrough atomic force microscope (AFM) and the averageroughness (Ra), root mean square element (Rq), profile height(Rmax) and depth (Rv) weremeasured. The open circuit potential(OCP), Potentiodynamic Polarization and electrochemicalimpedance spectroscopy (EIS) analysis were carried out at376 1°C in three electrodes electrochemical cell connected with(Gamry PC-14/750) Potentiostat. The saturated calomel(0.244VSHE) and graphite rod were used as reference andauxiliary electrodes respectively. For cell proliferation study, themesenchymal stem cells were aseptically isolated from the femurof Wistar rat. The bone marrow was flushed out by a syringecontaining a solution (10ml Dulbecco’s modified eagle mediumwith 10 per cent (Fetal Bovine Serum), 100U/ml penicillin and

100 mg/ml streptomycin). The 5 x105 MSCs were added in25cm2 cell culture flask and incubated under ‘controlled conditions’(humidified and 5 per cent CO2 environment at 37°C) for 24h.The washed stems cells (104) were initially added in a 6 well cellculture plate, containing flushing solution. Sterilized metalspecimens (heated at 180°C for 30min) were immediatelyseeded into the well and incubated under ‘controlled conditions’ for24 and 48h. The bright fieldmicroscopewas used to examine thecell morphology.

Results and discussion

The XRD patterns of Si-11, Si-12 and Si-13 are shown inFigure 1(a). The diffraction peaks matched with JCPDS 03-065-2585 and JCPDS 01-089-3721 reference patternscorresponding to ‘SiTi’ and ‘Ti5Si3’ phases respectively.Whereas other prominent peaks at 35.097°, 38.412°, 40.193°and 62.990° were characteristics to the a-Ti matrix phase butthe increase in peak intensity at 38.412° and genesis of theminor peak at 35.997° could be assigned to the Ti5Si3 and SiTiphases respectively. The significant increase in the peakintensity at 38.412° corresponded to the high density of (102)planes associated with Ti5Si3 phase. It was considered thatsmall radii ‘Si’ ions could penetrate within the subsurfacelattice sites of cp-Ti at high energy of ion beam (0.5MeV).The surface topography and surface roughness parameters of

B-01, Si-11, Si-12 and Si-13 are provided in Figure 1(b). Thefluence of high-energy ‘Si’ ions beam increased the ‘Ra’ and‘Rq’. Also, the topographical detail of Si-12 Figure 1(b)provided relatively larger ‘Rmax’ and ‘Rv’. This also suggestedthe nanoscale deformation of the surface due to ion fluence.Further increase in ions dose (Si-13), lowered the ‘Rmax’ and

Figure 1 Characterization of implanted samples

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‘Ry’ values which indicated local deformation of existingasperities by the repetitive bombardment of high concentrationincident ions.The open circuit potential (OCP) of B-01, Si-11, Si-12 and

Si-13 was measured in ringer‘s lactate solution as shown inFigure 2(a). The OCP of B-01 sampled was more negative(�0.2776 0.01VSHE) than implanted samples which exhibitedrelatively less negative potential. Interestingly, the Si-12 sample(0.0836 0.01VSHE) established positive (noble) potentialcompared to Si-11 and Si-13. From this behavior, it wasbelieved that the moderate (Si-12) dose level could be effectivetominimize corrosion tendency.To investigate electrochemical corrosion kinetic, the

potentiodynamic polarization scans were repeated thrice andthereminor deviation in the values but trends were almost sameFigure 2(b). The kinetics parameters were evaluated fromTafelregion and are given in Table I with 2-3 per cent standarddeviation from the mean values. The corrosion potential (Ecorr)shifted to positive direction after ion implantation and the shift

was more pronounced in the case of Si-12. Further increase inions dose, the polarization curve of Si-13 sample again shiftedto negative potential (Xiong et al., 2001). The anodicdissolution significantly decreased at higher ‘Si’ ions doses (Si-12, Si-13) compared to B-01 and Si-11. Also at intermediatedose level (for Si-12), the least negative ‘Ecorr’

(�0.0876 0.01VSHE), large ‘b a’ (0.851V/decade) and lower‘icorr’ (1.2260.025 mA.cm�2) than B-01, Si-11 and Si-13(Table I) also certified about three-fold decrease in corrosionrate.The Nyquist plots of B-01, Si-11, Si-12 and Si-13 were

simulated with the equivalent electrical circuit as shown inFigure 2(c). The lower relaxation coefficient (n = U/�90°)value (n< 1) was related to surface roughness andcorresponded to constant phase element (Yo). The appreciableincrease in charge transfer resistance “Rct” presented by Si-12and Si-13 (43.548kX-cm2 and 31.878kX-cm2 respectively)also provided evidence of their high corrosion resistance. Theseresults were in confirmation with the potentiodynamic

Figure 2 Electrochemical behavior of B-01, Si-11, Si-12 and Si-13

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Table I Electrochemical kinetic parameters calculated from the potentiodynamic polarization and impedance spectra

Sample Dose (Ions.cm�2) b a (V/dec) b c (V/dec) Ecorr(V)SHE i corr (mA/cm2) Rct (kX-cm2) Yo (mS.sncm�2) n CR (mpy)

B-01 � 0.742 0.225 �0.475 3.90 10.04 0.295 0.955 1.333Si-11 6.23� 1011 0.502 0.187 �0.309 3.61 7.951 191.372 0.515 1.651Si-12 6.54� 1012 0.851 0.176 �0.087 1.22 43.548 60.663 0.726 0.417Si-13 3.27� 1013 0.584 0.255 �0.255 1.36 31.878 66.977 0.669 0.466

Note: The data reported here are the mean values of the three tests and may have 2-3% standard deviation

Figure 3 The morphology and proliferation of stem cells

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polarization behavior. The higher corrosion rate (1.651mpy)and lower ‘Rct’ (7.951 kX-cm2) of Si-11 also identified theinferior corrosion resistance compared to Si-12 and Si-13.Form electrochemical tests it could be evaluated that themoderate dose (Si-12) would shift the OCP to noble value andsignificantly reduce the dissolution rate.The biological response of stem cells to B-01, Si-11, Si-12, and

Si-13 was evaluated during initial 24 and 48h incubation period.It was found that cell survival and proliferation exposed to thesesamples strongly depended on the surface chemistry andmorphology. Compared to controlled conditions, themorphology and proliferation characteristics of stem cells was lessaffected on Si-12 after 24 and 48h as shown in Figure 3(a)-(b)and (c)-(d), respectively. The mechanism of cell proliferation isdiscussed in detail elsewhere (Rahman et al., 2016).Briefly, the surface characteristics can directly affect the cell‘s

transmembrane receptors (Integrins) which consist of subunitsconsidered as the focal point for cell adhesion. The attachmentof these integrins is a function of surface chemistry andtopography (Xiong et al., 2001; Adam et al., 2006). Figure 3(e)represents the histogram of per cent cell viability undercontrolled and exposed (after seeding over samples) conditionsas a function of time. The cell proliferation over Si-12 wascomparable with the controlled culture media but the growth ofcells was adversely affected by B-01, Si-11 and Si-13 samples in48h. This inimical behavior could be related to the relativelyhigher dissolution of ions in the biological media which couldrestrict the protrusion of cells filopodia and limit proliferation.

Conclusion

The provenance of the minor peak at 35.997° in the XRDpatterns could be related to the formation of ‘SiTi’ and ‘Ti5Si3’phases at the surface. The low (Rmax) and (Rv) at the high dosewas attributed to the repetitive impact of ions and deformationof the existing asperities at the surface. The cp-Ti withintermediate dose (6.54� 1012ions.cm�2) displayed relativelynoble OCP, three-time lower corrosion rate, and four timeshigher ‘Rct’ compared to B-01. The potent biological responseat this dose was also confirmed from its higher cell viabilitycomparable to controlled proliferation in 24 and 48h. Thehigher dissolution tendency of Si-11 and Si-13 is suspected tonegatively affect the cell growth.

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Corresponding authorK.M. Deen can be contacted at: kashif_mairaj83@yahoo.com

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K.M. Deen, A. Farooq, M. Rizwan, A. Ahmad andW. Haider

Anti-Corrosion Methods and Materials

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